Async overlay is still shown even after blamer-mode is off

[daanturo]

When the async operation hasn't finished but blamer-mode is turned off, the commit info is still displayed and it stays there without going away (because the mode is off, auto-clear mechanics doesn't apply).

The sequence happens in this order:

1. post-command-hook triggers fetching git info asyncly (1)
2. (blamer-mode 0)
3. (1) returned and the commit info is displayed

Reproduce:

1. Evaluate

   (progn
   (defvar-local _count 0)
   (add-hook 'post-command-hook
           (lambda ()
             (cl-incf _count)
             ;; Use _count here because looks like pressing Enter in "M-:"
             ;; counts as executing a command
             (when (= 2 _count)
               (message "blamer off!")
               (blamer-mode 0)))
           nil 'local))

2. Do anything such as move the cursor once

Observed:

Commit info is displayed and doesn't go away.

Expected:

Commit info isn't displayed without blamer-mode.

[Artawower]

Thank you! One of the best pull request I've ever seen, with such a good explanation and reproduction steps! Really great job